Reference signal presence and/or bandwidth determination in narrowband systems

ABSTRACT

Aspects of the present disclosure provide techniques and apparatus for determining presence and/or bandwidth of reference signals (RS) in systems that utilize narrowband regions of wider system bandwidth for wireless communications, such as enhanced machine type communication(s) (eMTC) systems and/or narrowband Internet-of-Things (NB-IoT) systems. Aspects provide a method for wireless communications by a user equipment (UE) operating in a narrowband region of a wider system bandwidth. The method generally includes determining at least one of: a presence of one or more RS in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region; and monitoring for the one or more RS in the subframe based on the determination.

CROSS-REFERENCE TO RELATED APPLICATION & PRIORITY CLAIM

This application claims benefit of and priority to U.S. Provisional Patent Application Ser. No. 62/348,832, filed Jun. 10, 2016, which is herein incorporated by reference in its entirety for all applicable purposes.

BACKGROUND Field of the Disclosure

Certain aspects of the present disclosure generally relate to wireless communications and, more particularly, to reference signal presence and/or bandwidth determination in narrowband systems, such as enhanced machine type communication(s) (eMTC) systems and/or narrowband Internet-of-Things (NB-IoT) systems.

Description of Related Art

Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)/LTE-Advanced (LTE-A) systems and orthogonal frequency division multiple access (OFDMA) systems.

Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations (BSs) via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the BSs to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the BSs. This communication link may be established via a single-input single-output, multiple-input single-output or a multiple-input multiple-output (MIMO) system.

A wireless communication network may include a number of BSs that can support communication for a number of wireless devices. Wireless devices may include user equipments (UEs). Machine type communications (MTC) may refer to communication involving at least one remote device on at least one end of the communication and may include forms of data communication which involve one or more entities that do not necessarily need human interaction. MTC UEs may include UEs that are capable of MTC communications with MTC servers and/or other MTC devices through Public Land Mobile Networks (PLMN), for example. Wireless devices may include Internet-of-Things (IoT) devices (e.g., narrowband IoT (NB-IoT) devices). IoT may refer to a network of physical objects, devices, or “things”. IoT devices may be embedded with, for example, electronics, software, or sensors and may have network connectivity, which enable these devices to collect and exchange data.

Some next generation, NR, or 5G networks may include a number of base stations, each simultaneously supporting communication for multiple communication devices, such as UEs. In LTE or LTE-A network, a set of one or more BSs may define an e NodeB (eNB). In other examples (e.g., in a next generation or 5G network), a wireless multiple access communication system may include a number of distributed units (e.g., edge units (EUs), edge nodes (ENs), radio heads (RHs), smart radio heads (SRHs), transmission reception points (TRPs), etc.) in communication with a number of central units (e.g., CU, central nodes (CNs), access node controllers (ANCs), etc.), where a set of one or more distributed units (DUs), in communication with a CU, may define an access node (e.g., AN, a new radio base station (NR BS), a NR NB, a network node, a gNB, a 5G BS, an access point (AP), etc.). A BS or DU may communicate with a set of UEs on downlink channels (e.g., for transmissions from a BS or to a UE) and uplink channels (e.g., for transmissions from a UE to a BS or DU).

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. NR (e.g., 5G radio access) is an example of an emerging telecommunication standard. NR is a set of enhancements to the LTE mobile standard promulgated by 3GPP. NR is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL) as well as support beamforming, MIMO antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE, MTC, IoT, and NR technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

The systems, methods, and devices of the disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “DETAILED DESCRIPTION” one will understand how the features of this disclosure provide advantages that include improved communications between access points and stations in a wireless network.

Certain aspects of the present disclosure generally related to presence and/or bandwidth determination of reference signals in narrowband systems such as enhanced/evolved machine type communication(s) (eMTC) systems and/or narrowband Internet-of-Thing (NB-IoT) systems.

Certain aspects of the present disclosure provide a method for wireless communications by a user equipment (UE) operating in a narrowband region of a wider system bandwidth. The method generally includes determining at least one of: a presence of one or more reference signals (RS) in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region and monitoring for the one or more RS in the subframe based on the determination.

Certain aspects of the present disclosure provide a method for wireless communications by a base station (BS) for communication with a UE operating in a narrowband region of a wider system bandwidth. The method generally includes determining at least one of: a presence of one or more RS in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region; and transmitting the one or more RS in the subframe in at least the determined bandwidth.

Certain aspects of the present disclosure provide an apparatus for wireless communications by a UE operating in a narrowband region of a wider system bandwidth. The apparatus generally includes means for determining at least one of: a presence of one or more RS in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region and means for monitoring for the one or more RS in the subframe based on the determination.

Certain aspects of the present disclosure provide an apparatus for wireless communications by a BS for communication with a UE operating in a narrowband region of a wider system bandwidth. The apparatus generally includes means for determining at least one of: a presence of one or more RS in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region; and means for transmitting the one or more RS in the subframe in at least the determined bandwidth.

Certain aspects of the present disclosure provide an apparatus for wireless communications by a UE operating in a narrowband region of a wider system bandwidth. The apparatus generally includes at least one processor configured to determine at least one of: a presence of one or more RS in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region and a receiver configured to monitor for the one or more RS in the subframe based on the determination.

Certain aspects of the present disclosure provide an apparatus for wireless communications by a BS for communication with a UE operating in a narrowband region of a wider system bandwidth. The apparatus generally includes at least one processor configured to determine at least one of: a presence of one or more RS in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region; and a transmitter configured to transmit the one or more RS in the subframe in at least the determined bandwidth.

Certain aspects of the present disclosure provide a computer readable medium having computer executable code stored thereon for wireless communications by a UE operating in a narrowband region of a wider system bandwidth. The computer executable code generally includes code for determining at least one of: a presence of one or more RS in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region and code for monitoring for the one or more RS in the subframe based on the determination.

Certain aspects of the present disclosure provide a computer readable medium having computer executable code stored thereon for wireless communications by a BS for communication with a UE operating in a narrowband region of a wider system bandwidth. The computer executable code generally includes code for determining at least one of: a presence of one or more RS in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region; and code for transmitting the one or more RS in the subframe in at least the determined bandwidth.

Numerous other aspects are provided including methods, apparatus, systems, computer program products, computer-readable medium, and processing systems capable of performing the operations described above. To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.

FIG. 1 is a block diagram conceptually illustrating an example of a wireless communication network, in accordance with certain aspects of the present disclosure.

FIG. 2 shows a block diagram conceptually illustrating an example of a base station (BS) in communication with a user equipment (UE) in a wireless communications network, in accordance with certain aspects of the present disclosure.

FIG. 3 is a block diagram conceptually illustrating an example of a frame structure in a wireless communications network, in accordance with certain aspects of the present disclosure.

FIG. 4 is a block diagram conceptually illustrating two exemplary subframe formats with the normal cyclic prefix, in accordance with certain aspects of the present disclosure.

FIG. 5 illustrates an exemplary subframe configuration for enhanced/evolved machine type communications (eMTC), in accordance with certain aspects of the present disclosure.

FIG. 6 illustrates an example deployment of narrowband Internet-of-Things (NB-IoT), in accordance with certain aspects of the present disclosure.

FIG. 7 illustrates an example logical architecture of a distributed radio access network (RAN), in accordance with certain aspects of the present disclosure.

FIG. 8 illustrates an example physical architecture of a distributed RAN, in accordance with certain aspects of the present disclosure.

FIG. 9 is a diagram illustrating an example of a downlink (DL)-centric subframe, in accordance with certain aspects of the present disclosure.

FIG. 10 is a diagram illustrating an example of an uplink (UL)-centric subframe, in accordance with certain aspects of the present disclosure.

FIG. 11 is a flow diagram illustrating example operations for wireless communications by a UE, in accordance with certain aspects of the present disclosure.

FIG. 12 is a flow diagram illustrating example operations for wireless communications by a BS, in accordance with certain aspects of the present disclosure.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized on other aspects without specific recitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques for determining (and/or signaling) presence and/or bandwidth used for transmission of reference signals (RS) in systems with devices that communicate using narrowband regions of a wider system bandwidth, such as enhanced/evolved machine type communication(s) (eMTC) systems and/or narrowband Internet-of-Things (NB-IoT) systems.

The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as universal terrestrial radio access (UTRA), cdma2000, etc. UTRA includes wideband CDMA (WCDMA), time division synchronous CDMA (TD-SCDMA), and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as global system for mobile communications (GSM). An OFDMA network may implement a radio technology such as evolved UTRA (E-UTRA), ultra mobile broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part of universal mobile telecommunication system (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A), in both frequency division duplex (FDD) and time division duplex (TDD), are new releases of UMTS that use E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). NR (e.g., 5G radio access) is an example of an emerging telecommunication standard. NR is a set of enhancements to the LTE mobile standard promulgated by 3GPP. The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. Certain aspects of the techniques are described below for LTE/LTE-Advanced (LTE-A), and LTE/LTE-A terminology is used in much of the description below. LTE and LTE-A are referred to generally as LTE.

It is noted that while aspects may be described herein using terminology commonly associated with 3G and/or 4G wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems, such as 5G and later.

Example Wireless Communications Network

FIG. 1 illustrates an example wireless communication network 100, in which aspects of the present disclosure may be practiced. For example, techniques presented herein may be used for determining and/or signaling presence and/or bandwidth of reference signals (RS) in narrowband systems, such as enhanced/evolved machine type communication(s) (eMTC) and/or narrowband internet-of-things (NB-IoT).

For example, wireless communication network 100 may include base stations (BS) 110 and user equipment (UEs) 120. In aspects, a BS 110 can determine presence of RS in a subframe and/or the bandwidth of the RS. BS 110 can transmit the RS in the subframe in at least the determined bandwidth. UE 120, which may be an eMTC device, low cost UE, or NB-IoT device, can determine the presence of the RS in the subframe and/or the bandwidth of the RS and monitor (decode/receive) for the RS in the subframe based on the determination.

Wireless communication network 100 may be a long term evolution (LTE) network or some other wireless network, such as a new radio (NR) or 5G access network. Wireless communication network 100 may include a number of BSs 110 and other network entities. A BS is an entity that communicates with UEs and may also be referred to as a Node B (NB), an enhanced/evolved NB (eNB), a gNB, a 5G NB, an access point (AP), NR BS, transmission reception point (TRP), etc. Each BS may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of a BS and/or a BS subsystem serving this coverage area, depending on the context in which the term is used.

A BS may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having association with the femto cell (e.g., UEs in a closed subscriber group (CSG)). n BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS. In the example shown in FIG. 1, BS 110 a may be a macro BS for a macro cell 102 a, BS 110 b may be a pico BS for a pico cell 102 b, and BS 110 c may be a femto BS for a femto cell 102 c. A BS may support one or multiple (e.g., three) cells. The terms “base station” and “cell” may be used interchangeably herein.

Wireless communication network 100 may also include relay stations. A relay station is an entity that can receive a transmission of data from an upstream station (e.g., BS 110 or a UE 120) and send a transmission of the data to a downstream station (e.g., UE 120 or BS 110). A relay station may also be a UE that can relay transmissions for other UEs. In the example shown in FIG. 1, relay station 110 d may communicate with macro BS 110 a and UE 120 d in order to facilitate communication between BS 110 a and UE 120 d. A relay station may also be referred to as a relay eNB, a relay BS, a relay, etc.

Wireless communication network 100 may be a heterogeneous network that includes BSs of different types, e.g., macro BSs, pico BSs, femto BSs, relay BSs, etc. These different types of BSs may have different transmit power levels, different coverage areas, and different impact on interference in wireless communication network 100. For example, macro BSs may have a high transmit power level (e.g., 5 to 40 Watts) whereas pico BSs, femto BSs, and relay BSs may have lower transmit power levels (e.g., 0.1 to 2 Watts).

Network controller 130 may couple to a set of BSs and may provide coordination and control for these BSs. Network controller 130 may communicate with the BSs via a backhaul. The BSs may also communicate with one another, e.g., directly or indirectly via a wireless or wireline backhaul.

UEs 120 (e.g., UE 120 a, UE 120 b, UE 120 c) may be dispersed throughout wireless communication network 100, and each UE may be stationary or mobile. A UE may also be referred to as an access terminal, a terminal, a mobile station, a subscriber unit, a station, a Customer Premises Equipment (CPE), etc. A UE may be a cellular phone (e.g., a smart phone), a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet, a camera, a gaming device, a netbook, a smartbook, an ultrabook, a medical device, medical equipment, a biometric sensor/device, a wearable device such as a smart watch, smart clothing, smart glasses, a smart wristband, and/or smart jewelry (e.g., a smart ring, a smart bracelet, etc.), an entertainment device (e.g., a music device, a video device, a satellite radio, etc.), industrial manufacturing equipment, a global positioning system (GPS) device, or any other suitable device configured to communicate via a wireless or wired medium. Some UEs may be considered machine-type communication (MTC) devices or enhanced/evolved MTC (eMTC) devices. MTC/eMTC UEs may be implemented as IoT UEs. IoT UEs include, for example, robots/robotic devices, drones, remote devices, sensors, meters, monitors, cameras, location tags, etc., that may communicate with a BS, another device (e.g., remote device), or some other entity. A wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as Internet or a cellular network) via a wired or wireless communication link.

One or more UEs 120 in the wireless communication network 100 (e.g., an LTE network) may be a narrowband bandwidth UE (e.g., eMTC and/or NB-IoT UEs). As used herein, devices with limited communication resources, e.g. smaller bandwidth, may be referred to generally as narrowband UEs. Similarly, legacy devices, such as legacy and/or advanced UEs (e.g., in LTE) may be referred to generally as wideband UEs. Generally, wideband UEs are capable of operating on a larger amount of bandwidth than narrowband UEs.

In FIG. 1, a solid line with double arrows indicates desired transmissions between a UE and a serving BS, which is a BS designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates potentially interfering transmissions between a UE and a BS.

In general, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a particular radio access technology (RAT) and may operate on one or more frequencies. A RAT may also be referred to as a radio technology, an air interface, etc. A frequency may also be referred to as a carrier, a frequency channel, etc. Each frequency may support a single RAT in a given geographic area in order to avoid interference between wireless networks of different RATs. In some cases, NR or 5G RAT networks may be deployed.

In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a BS 110) allocates resources for communication among some or all devices and equipment within its service area or cell. The scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. For scheduled communication, subordinate entities utilize resources allocated by the scheduling entity. BSs 110 are not the only entities that may function as a scheduling entity. In some examples, UE 120 may function as a scheduling entity, scheduling resources for one or more subordinate entities (e.g., one or more other UEs 120). In this example, the UE is functioning as a scheduling entity, and other UEs utilize resources scheduled by the UE for wireless communication. A UE may function as a scheduling entity in a peer-to-peer (P2P) network, and/or in a mesh network. In a mesh network example, UEs may optionally communicate directly with one another in addition to communicating with the scheduling entity.

Thus, in a wireless communication network with a scheduled access to time-frequency resources and having a cellular configuration, a P2P configuration, and a mesh configuration, a scheduling entity and one or more subordinate entities may communicate utilizing the scheduled resources.

FIG. 2 shows a block diagram of a design of BS 110 and UE 120, which may be one of the BSs and one of the UEs shown in FIG. 1. BS 110 may be equipped with T antennas 234 a through 234 t, and UE 120 may be equipped with R antennas 252 a through 252 r, where in general T≧1 and R≧1.

At BS 110, transmit processor 220 may receive data from data source 212 for one or more UEs, select one or more modulation and coding schemes (MCS) for each UE based on channel quality indicators (CQIs) received from the UE, process (e.g., encode and modulate) the data for each UE based on the MCS(s) selected for the UE, and provide data symbols for all UEs. Transmit processor 220 may also process system information (e.g., for static resource partitioning information (SRPI), etc.) and control information (e.g., CQI requests, grants, upper layer signaling, etc.) and provide overhead symbols and control symbols. Processor 220 may also generate reference symbols for reference signals (e.g., the cell-specific reference signal (CRS)) and synchronization signals (e.g., the primary synchronization signal (PSS) and secondary synchronization signal (SSS)). Transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, the overhead symbols, and/or the reference symbols, if applicable, and may provide T output symbol streams to T modulators (MODs) 232 a through 232 t. Each modulator 232 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 232 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. T downlink signals from modulators 232 a through 232 t may be transmitted via T antennas 234 a through 234 t, respectively.

At UE 120, antennas 252 a through 252 r may receive the downlink signals from BS 110 and/or other BSs and may provide received signals to demodulators (DEMODs) 254 a through 254 r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, and digitize) its received signal to obtain input samples. Each demodulator 254 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. MIMO detector 256 may obtain received symbols from all R demodulators 254 a through 254 r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. Receive processor 258 may process (e.g., demodulate and decode) the detected symbols, provide decoded data for UE 120 to data sink 260, and provide decoded control information and system information to controller/processor 280. A channel processor may determine reference signal received power (RSRP), receive signal strength indicator (RSSI), reference signal received quality (RSRQ), CQI, etc.

On the uplink, at UE 120, transmit processor 264 may receive and process data from data source 262 and control information (e.g., for reports comprising RSRP, RSSI, RSRQ, CQI, etc.) from controller/processor 280. Processor 264 may also generate reference symbols for one or more reference signals. The symbols from transmit processor 264 may be precoded by TX MIMO processor 266 if applicable, further processed by modulators 254 a through 254 r (e.g., for SC-FDM, OFDM, etc.), and transmitted to BS 110. At BS 110, the uplink signals from UE 120 and other UEs may be received by antennas 234, processed by demodulators 232, detected by MIMO detector 236 if applicable, and further processed by receive processor 238 to obtain decoded data and control information sent by UE 120. Processor 238 may provide the decoded data to data sink 239 and the decoded control information to controller/processor 240. BS 110 may include communication unit 244 and communicate to network controller 130 via communication unit 244. Network controller 130 may include communication unit 294, controller/processor 290, and memory 292.

Controllers/processors 240 and 280 may direct the operation at BS 110 and UE 120, respectively, to perform techniques presented herein. For example, processor 240 and/or other processors and modules at BS 110, and processor 280 and/or other processors and modules at UE 120, may perform or direct operations of BS 110 and UE 120, respectively. For example, controller/processor 280 and/or other controllers/processors and modules at UE 120, and/or controller/processor 240 and/or other controllers/processors and modules at BS 110 may perform or direct operations 1100 and 1200 shown in FIGS. 11 and 12, respectively. Memories 242 and 282 may store data and program codes for BS 110 and UE 120, respectively. Scheduler 246 may schedule UEs for data transmission on the downlink and/or uplink.

FIG. 3 shows an exemplary frame structure 300 for frequency division duplexing (FDD) in a wireless communication systems (e.g., such as wireless communication network 100). The transmission timeline for each of the downlink and uplink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be partitioned into 10 subframes with indices of 0 through 9. Each subframe may include two slots. Each radio frame may thus include 20 slots with indices of 0 through 19. Each slot may include L symbol periods, for example, seven symbol periods for a normal cyclic prefix (as shown in FIG. 3) or six symbol periods for an extended cyclic prefix. The 2L symbol periods in each subframe may be assigned indices of 0 through 2L−1.

In certain wireless communication systems (e.g., LTE), a BS may transmit a PSS and a SSS on the downlink in the center of the system bandwidth for each cell supported by the BS. The PSS and SSS may be transmitted in symbol periods 6 and 5, respectively, in subframes 0 and 5 of each radio frame with the normal cyclic prefix, as shown in FIG. 3. The PSS and SSS may be used by UEs for cell search and acquisition. The BS may transmit a CRS across the system bandwidth for each cell supported by the BS. The CRS may be transmitted in certain symbol periods of each subframe and may be used by the UEs to perform channel estimation, channel quality measurement, and/or other functions. The BS may also transmit a physical broadcast channel (PBCH) in symbol periods 0 to 3 in slot 1 of certain radio frames. The PBCH may carry some system information. The BS may transmit other system information such as system information blocks (SIBs) on a physical downlink shared channel (PDSCH) in certain subframes. The BS may transmit control information/data on a physical downlink control channel (PDCCH) in the first B symbol periods of a subframe, where B may be configurable for each subframe. The BS may transmit traffic data and/or other data on the PDSCH in the remaining symbol periods of each subframe.

In certain systems (e.g., such as NR or 5G systems), a BS may transmit these or other signals in these locations or in different locations of the subframe.

FIG. 4 shows two exemplary subframe formats 410 and 420 with the normal cyclic prefix. The available time frequency resources may be partitioned into resource blocks (RBs). Each RB may cover 12 subcarriers in one slot and may include a number of resource elements (RE). Each RE may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value.

Subframe format 410 may be used for two antennas. A CRS may be transmitted from antennas 0 and 1 in symbol periods 0, 4, 7 and 11. A reference signal is a signal that is known a priori by a transmitter and a receiver and may also be referred to as pilot. A CRS is a reference signal that is specific for a cell, e.g., generated based on a cell identity (ID). In FIG. 4, for a given RE with label Ra, a modulation symbol may be transmitted on that RE from antenna a, and no modulation symbols may be transmitted on that RE from other antennas. Subframe format 420 may be used with four antennas. A CRS may be transmitted from antennas 0 and 1 in symbol periods 0, 4, 7 and 11 and from antennas 2 and 3 in symbol periods 1 and 8. For both subframe formats 410 and 420, a CRS may be transmitted on evenly spaced subcarriers, which may be determined based on cell ID. CRSs may be transmitted on the same or different subcarriers, depending on their cell IDs. For both subframe formats 410 and 420, REs not used for the CRS may be used to transmit data (e.g., traffic data, control data, and/or other data).

The PSS, SSS, CRS and PBCH in LTE are described in 3GPP TS 36.211, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation,” which is publicly available.

An interlace structure may be used for each of the downlink and uplink for FDD (e.g., in LTE). For example, Q interlaces with indices of 0 through Q−1 may be defined, where Q may be equal to 4, 6, 8, 10, or some other value. Each interlace may include subframes that are spaced apart by Q frames. In particular, interlace q may include subframes q, q+Q, q+2Q, etc., where q ∈{0, . . . ,Q−1}.

The wireless communication network (e.g., wireless communication network 100) may support hybrid automatic retransmission request (HARQ) for data transmission on the downlink and uplink. For HARQ, a transmitter (e.g., a BS such as a BS 110) may send one or more transmissions of a packet until the packet is decoded correctly by a receiver (e.g., a UE such as a UE 120) or some other termination condition is encountered. For synchronous HARQ, all transmissions of the packet may be sent in subframes of a single interlace. For asynchronous HARQ, each transmission of the packet may be sent in any subframe.

A UE may be located within the coverage of multiple BSs. One of these BSs may be selected to serve the UE. The serving BS may be selected based on various criteria such as received signal strength, received signal quality, pathloss, etc. Received signal quality may be quantified by a signal-to-noise-and-interference ratio (SINR), or a RSRQ, or some other metric. The UE may operate in a dominant interference scenario in which the UE may observe high interference from one or more interfering BS.

Example Narrowband Communications

The wireless communication network may support a 180 kHz deployment for narrowband operation (such as, for example, narrowband interne of things (NB-IoT)) with different deployment modes. In one example, narrowband operations may be deployed in-band, for example, using resource blocks (RBs) within a wider system bandwidth. In one case, narrowband operations may use one RB within the wider system bandwidth of an existing network, for example, such as a long term evolution (LTE) network. In this case, the 180 kHz bandwidth for the RB may have to be aligned with a wideband RB. In one example, narrowband operations may be deployed in the unused RBs within a carrier guard-band (e.g., LTE). In this deployment, the 180 kHz RB within the guard band may be aligned with a 15 kHz tone grid of wideband LTE, for example, in order to use the same Fast Fourier Transform (FFT) and/or reduce interference in-band legacy LTE communications.

The focus of traditional LTE design (e.g., for legacy “non-MTC” and/or “non-IoT” devices) is on the improvement of spectral efficiency, ubiquitous coverage, and enhanced quality of service (QoS) support. Current LTE system downlink and uplink link budgets are designed for coverage of high end devices, such as state-of-the-art smartphones and tablets, which may support a relatively large downlink and uplink link budget.

However, as described above, one or more UEs in the wireless communication network (e.g., wireless communication network 100) may be low cost devices that have limited communication resources, such as narrowband UEs, as compared to other (wideband) devices in the wireless communication network. For narrowband UEs, various requirements may be relaxed as only a limited amount of information may need to be exchanged. For example, maximum bandwidth may be reduced (relative to wideband UEs), a single receive radio frequency (RF) chain may be used, peak rate may be reduced (e.g., a maximum of 1000 bits for a transport block size), transmit power may be reduced, Rank 1 transmission may be used, and half-duplex operation may be performed.

In some cases, if half-duplex operation is performed, MTC UEs may have a relaxed switching time to transition from transmitting to receiving (or receiving to transmitting). For example, the switching time may be relaxed from 20 μs for regular UEs to 1 ms for MTC UEs. Release 12 MTC UEs may still monitor downlink control channels in the same way as regular UEs, for example, by monitoring for wideband control channels in the first few symbols (e.g., the physical downlink control channel (PDCCH)) as well as narrowband control channels occupying a relatively narrowband, but spanning a length of a subframe (e.g., enhanced PDCCH (ePDCCH)).

Certain standards (e.g., LTE Release 13) may introduce support for various additional MTC enhancements, referred to herein as eMTC. For example, eMTC may provide UEs with coverage enhancements up to 15 dB or better.

As illustrated in the subframe structure 500 of FIG. 5, eMTC UEs can support narrowband operation while operating in a wider system bandwidth (e.g., 1.4/3/5/10/15/20 MHz). In the example illustrated in FIG. 5, a conventional legacy control region 510 may span system bandwidth of a first few symbols, while a narrowband region 530 of the system bandwidth (spanning a narrow portion of a data region 520) may be reserved for an MTC PDCCH (MPDCCH) and for an MTC physical downlink shared channel (MPDSCH). In some cases, an (e)MTC UE monitoring the narrowband region may operate at 1.4 MHz or 6 RBs. The MPDCCH may rely on demodulation reference signal (DMRS) demodulation. Coverage may be increased by performing repetition/bundling of signals.

However, as noted above, eMTC UEs may be able to operate in a cell with a bandwidth larger than 6 RBs. Within this larger bandwidth, each eMTC UE may still operate (e.g., monitor/receive/transmit) while abiding by a 6-PRB constraint. In some cases, different eMTC UEs may be served by different narrowband regions (e.g., with each spanning 6-PRB blocks). Because the system bandwidth may span from 1.4 MHz to 20 MHz, or from 6 RBs to 100 RBs, multiple narrowband regions may exist within the larger bandwidth. An eMTC UE may switch or hop between multiple narrowband regions in order to reduce interference.

The Internet-of-Things (IoT) may refer to a network of physical objects, devices, or “things”. IoT devices may be embedded with, for example, electronics, software, or sensors and may have network connectivity, which enable these devices to collect and exchange data. IoT devices may be sensed and controlled remotely across existing network infrastructure, creating opportunities for more direct integration between the physical world and computer-based systems and resulting in improved efficiency, accuracy, and economic benefit. Systems that include IoT devices augmented with sensors and actuators may be referred to cyber-physical systems. Cyber-physical systems may include technologies such as smart grids, smart homes, intelligent transportation, and/or smart cities. Each “thing” (e.g., IoT device) may be uniquely identifiable through its embedded computing system may be able to interoperate within existing infrastructure, such as Internet infrastructure.

Certain wireless communication systems (e.g., wireless communication network 100), such as LTE Release 13) may support narrowband IoT (NB-IoT) operation. NB-IoT may refer to a narrowband radio technology designed for IoT. NB-IoT may focus on indoor coverage, low cost, long batter life, and large number of devices. To reduce the complexity of UEs, NB-IoT may allow for narrowband deployments utilizing one PRB (e.g., 180 kHz+20 kHz guard band).

NB-IoT may offer standalone, in-band, or guard band deployment scenarios. Standalone deployment may use new bandwidth, whereas guard band deployment may be done using bandwidth typically reserved in the guard band of an existing network, such as long term evolution (LTE). In-band deployment on the other hand may use the same resource blocks in the LTE carrier of the existing LTE network. NB-IoT may offer increased coverage. NB-IoT may define a new narrowband control channel (e.g., NPDCCH), data (e.g., PDSCH), and references signals (e.g., NRS) that fit in 1 RB.

FIG. 6 illustrates an example deployment 600 of NB-IoT, according to certain aspects of the present disclosure. Three NB-IoT deployment configurations include in-band, guard-band, and standalone. For the in-band deployment configuration, NB-IoT may coexist with a legacy system (e.g., GSM, WCDMA, and/or LTE system(s)) deployed in the same frequency band. For example, the wideband LTE channel may be deployed in various bandwidths between 1.4 MHz to 20 MHz. As shown in FIG. 6, a dedicated RB 602 within that bandwidth may be available for use by NB-IoT and/or the RBs 1204 may be dynamically allocated for NB-IoT. As shown in FIG. 6, in an in-band deployment, one RB, or 200 kHz, of a wideband channel (e.g., LTE) may be used for NB-IoT.

Certain systems (e.g., LTE) may include unused portions of the radio spectrum between carriers to guard against interference between adjacent carriers. In some deployments, NB-IoT may be deployed in a guard band 606 of the wideband channel.

In other deployments, NB-IoT may be deployed standalone (not shown). In a standalone deployment, one 200 MHz carrier may be utilized to carry NB-IoT traffic and GSM spectrum may be reused.

Deployments of NB-IoT may include synchronization signals such as PSS for frequency and timing synchronization and SSS to convey system information. For NB-IoT operations, PSS/SSS timing boundaries may be extended as compared to the existing PSS/SSS frame boundaries in legacy systems (e.g., LTE), for example, from 10 ms to 40 ms. Based on the timing boundary, a UE is able to receive a PBCH transmission, which may be transmitted in subframe 0 of a radio frame.

Example NR/5G RAN Architecture

New radio (NR) may refer to radios configured to operate according to a new air interface (e.g., other than Orthogonal Frequency Divisional Multiple Access (OFDMA)-based air interfaces) or fixed transport layer (e.g., other than Internet Protocol (IP)). NR may utilize OFDM with a CP on the uplink and downlink and include support for half-duplex operation using TDD. NR may include Enhanced Mobile Broadband (eMBB) service targeting wide bandwidth (e.g. 80 MHz beyond), millimeter wave (mmW) targeting high carrier frequency (e.g. 60 GHz), massive MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra reliable low latency communications (URLLC) service.

A single component carrier (CC) bandwidth of 100 MHZ may be supported. NR RBs may span 12 sub-carriers with a sub-carrier bandwidth of 75 kHz over a 0.1 ms duration. Each radio frame may consist of 50 subframes with a length of 10 ms. Consequently, each subframe may have a length of 0.2 ms. Each subframe may indicate a link direction (e.g., DL or UL) for data transmission and the link direction for each subframe may be dynamically switched. Each subframe may include DL/UL data as well as DL/UL control data. UL and DL subframes for NR may be as described in more detail below with respect to FIGS. 9 and 10.

Beamforming may be supported and beam direction may be dynamically configured. MIMO transmissions with precoding may also be supported. MIMO configurations in the DL may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells. Alternatively, NR may support a different air interface, other than an OFDM-based interface. NR networks may include entities such central units (CUs) or distributed units (DUs).

The NR RAN may include a CU and DUs. A NR BS (e.g., a NB, an eNB, a gNB, a 5G NB, a TRP, an AP, etc.) may correspond to one or multiple BSs. NR cells can be configured as access cells (ACells) or data only cells (DCells). For example, the RAN (e.g., a CU or DU) can configure the cells. DCells may be cells used for carrier aggregation or dual connectivity, but not used for initial access, cell selection/reselection, or handover. In some cases DCells may not transmit synchronization signals—in some case cases DCells may transmit synchronization signals.

FIG. 7 illustrates an example logical architecture 700 of a distributed RAN, according to aspects of the present disclosure. 5G access node 706 may include access node controller (ANC) 702. ANC 702 may be a CU of the distributed RAN. The backhaul interface to the next generation core network (NG-CN) 704 may terminate at ANC 702. The backhaul interface to neighboring next generation access nodes (NG-ANs) 710 may terminate at ANC 702. ANC 702 may include one or more TRPs 708. As described above, TRP may be used interchangeably with “cell”, BS, NR BS, NB, eNB, 5G NB, gNB, AP, etc.

TRPs 708 may comprise a DU. TRPs 708 may be connected to one ANC (e.g., ANC 702) or more than one ANC (not illustrated). For example, for RAN sharing, radio as a service (RaaS), and service specific AND deployments, TRP 708 may be connected to more than one ANC. TRP 708 may include one or more antenna ports. TRPs 708 may be configured to individually (e.g., dynamic selection) or jointly (e.g., joint transmission) serve traffic to a UE.

Logical architecture 700 may be used to illustrate fronthaul definition. The architecture may be defined that support fronthauling solutions across different deployment types. For example, logical architecture 700 may be based on transmit network capabilities (e.g., bandwidth, latency, and/or jitter). Logical architecture 700 may share features and/or components with LTE. According to aspects, NG-AN 710 may support dual connectivity with NR. NG-AN 710 may share a common fronthaul for LTE and NR. Logical architecture 700 may enable cooperation between and among TRPs 708. For example, cooperation may be preset within a TRP and/or across TRPs via ANC 702. In some cases, no inter-TRP interface may be needed/present.

A dynamic configuration of split logical functions may be present within logical architecture 700. The packet data convergence protocol (PDCP), radio link control (RLC), and medium access control (MAC) protocols may be adaptably placed at ANC 702 or TRP 708.

FIG. 8 illustrates an example physical architecture 800 of a distributed RAN, according to aspects of the present disclosure. Centralized core network unit (C-CU) 802 may host core network functions. C-CU 802 may be centrally deployed. C-CU 802 functionality may be offloaded (e.g., to advanced wireless services (AWS)), in an effort to handle peak capacity.

Centralized RAN unit (C-RU) 804 may host one or more ANC functions. Optionally, C-RU 804 may host core network functions locally. C-RU 804 may have distributed deployment. C-RU 804 may be closer to the network edge.

DU 806 may host one or more TRPs. DU 806 may be located at edges of the network with radio frequency (RF) functionality.

FIG. 9 is a diagram showing an example of a DL-centric subframe 900. DL-centric subframe 900 may include control portion 902. Control portion 902 may exist in the initial or beginning portion of DL-centric subframe 900. Control portion 902 may include various scheduling information and/or control information corresponding to various portions of DL-centric subframe 900. In some configurations, control portion 902 may be a physical DL control channel (PDCCH), as shown in FIG. 9. DL-centric subframe 900 may also include DL data portion 904. DL data portion 904 may sometimes be referred to as the payload of DL-centric subframe 900. DL data portion 904 may include the communication resources utilized to communicate DL data from the scheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE). In some configurations, DL data portion 904 may be a physical DL shared channel (PDSCH).

DL-centric subframe 900 may also include common UL portion 906. Common UL portion 906 may sometimes be referred to as an UL burst, a common UL burst, and/or various other suitable terms. Common UL portion 906 may include feedback information corresponding to various other portions of DL-centric subframe 900. For example, common UL portion 906 may include feedback information corresponding to control portion 902. Non-limiting examples of feedback information may include an acknowledgment (ACK) signal, a negative acknowledgment (NACK) signal, a HARQ indicator, and/or various other suitable types of information. Common UL portion 906 may include additional or alternative information, such as information pertaining to random access channel (RACH) procedures, scheduling requests (SRs), and various other suitable types of information. As illustrated in FIG. 9, the end of DL data portion 904 may be separated in time from the beginning of common UL portion 906. This time separation may sometimes be referred to as a gap, a guard period, a guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the subordinate entity) to UL communication (e.g., transmission by the subordinate entity). One of ordinary skill in the art will understand that the foregoing is merely one example of a DL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

FIG. 10 is a diagram showing an example of UL-centric subframe 1000. UL-centric subframe 1000 may include control portion 1002. Control portion 1002 may exist in the initial or beginning portion of UL-centric subframe 1000. Control portion 1002 in FIG. 10 may be similar to control portion 1002 described above with reference to FIG. 9. UL-centric subframe 1000 may also include UL data portion 1004. UL data portion 1004 may sometimes be referred to as the payload of UL-centric subframe 1000. The UL portion may refer to the communication resources utilized to communicate UL data from the subordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS). In some configurations, control portion 1002 may be a PDCCH. In some configurations, the data portion may be a physical uplink shared channel (PUSCH).

As illustrated in FIG. 10, the end of control portion 1002 may be separated in time from the beginning of UL data portion 1004. This time separation may sometimes be referred to as a gap, guard period, guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the scheduling entity) to UL communication (e.g., transmission by the scheduling entity). UL-centric subframe 1000 may also include common UL portion 1006. Common UL portion 1006 in FIG. 10 may be similar to common UL portion 906 described above with reference to FIG. 9. Common UL portion 1006 may additionally or alternatively include information pertaining to CQI, sounding reference signals (SRSs), and various other suitable types of information. One of ordinary skill in the art will understand that the foregoing is merely one example of an UL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

In some circumstances, two or more subordinate entities (e.g., UEs) may communicate with each other using sidelink signals. Real-world applications of such sidelink communications may include public safety, proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V) communications, Internet of Everything (IoE) communications, IoT communications, mission-critical mesh, and/or various other suitable applications. Generally, a sidelink signal may refer to a signal communicated from one subordinate entity (e.g., UE1) to another subordinate entity (e.g., UE2) without relaying that communication through the scheduling entity (e.g., UE or BS), even though the scheduling entity may be utilized for scheduling and/or control purposes. In some examples, the sidelink signals may be communicated using a licensed spectrum (unlike wireless local area networks, which typically use an unlicensed spectrum).

A UE may operate in various radio resource configurations, including a configuration associated with transmitting pilots using a dedicated set of resources (e.g., a RRC dedicated state, etc.) or a configuration associated with transmitting pilots using a common set of resources (e.g., an RRC common state, etc.). When operating in the RRC dedicated state, the UE may select a dedicated set of resources for transmitting a pilot signal to a network. When operating in the RRC common state, the UE may select a common set of resources for transmitting a pilot signal to the network. In either case, a pilot signal transmitted by the UE may be received by one or more network access devices, such as an AN, a DU, or portions thereof. Each receiving network access device may be configured to receive and measure pilot signals transmitted on the common set of resources, and also receive and measure pilot signals transmitted on dedicated sets of resources allocated to the UEs for which the network access device is a member of a monitoring set of network access devices for the UE. One or more of the receiving network access devices, or a CU to which receiving network access device(s) transmit the measurements of the pilot signals, may use the measurements to identify serving cells for the UEs, or to initiate a change of serving cell for one or more of the UEs.

Example Reference Signal Presence and/or Bandwidth Determination in Narrowband Systems

Narrowband devices (e.g., in a wireless communication system such as wireless communication network 100), including eMTC devices and/or NB-IoT devices (e.g., such as a UE 120), may use reference signals (RS), transmitted from a base station (BS) (e.g., such as a BS 110), for various purposes. For example, eMTC devices may use cell-specific reference signals (CRS) for channel estimation, frequency and time tracking, and the like. NB-IoT devices may use narrowband reference signals (NB-RS or NRS) and possibly CRS for channel estimation, frequency and time tracking, and the like (e.g., if the same PCI index/indication is set to ‘1’).

The channel estimation may be based on a narrowband observation (e.g., the reference signal used) that may be the same as the nominal narrowband channel bandwidth or slightly wider. In other words, the UE may be configured for narrowband operation (e.g., 6 RB for eMTC or 1 RB for NB-IoT) and the reference signal may sometimes be sent at that bandwidth or at a greater bandwidth (i.e., greater than 1 RB or greater than 6 RB). If the RS is sent at a greater bandwidth than the nominal narrowband channel bandwidth, the UE may assume that the RS (e.g., CRS) is present outside of the assigned narrowband region.

In order to reduce interference to other cells and to save power, the BS may configure some subframes as MBSFN (multicast/multimedia broadcast single frequency network) subframes, as evolved multimedia broadcast multicast service (eMBMS) subframes having a longer cyclic prefix (CP), or as blank subframes (e.g., in a new carrier type). These subframes can be signaled as invalid subframes for narrowband devices, such as eMTC UEs and/or NB-IoT UEs. Alternatively, these subframes can be signaled as valid subframes for the narrowband devices, and additional narrowband reference signals can be inserted (e.g., transmitted) in those subframes for use by the narrowband devices. As used in this context “valid” may refer to the inclusion of reference signals for these types of UEs, while “invalid” may refer to a lack of such reference signals.

In some cases, for a given subframe, a UE may not know (e.g., it may be ambiguous) whether RS are present in that subframe and/or the UE may not know the bandwidth of the RS in the subframe.

The following examples of subframe configurations for eMTC may result in an ambiguity for the UE as to the presence of RS and/or the bandwidth used for sending RS in the subframe. In an example, a subframe may be configured as a valid and non-MBSFN subframe for eMTC UEs, but the subframe is configured as an MBSFN subframe, long CP eMBMS subframe, or blank subframe for other UEs. Narrowband CRS may be transmitted in symbols 4, 7, and 11 in the subframe in the 6 RB narrowband region (also in symbol 0 in the case that the subframe is configured as eMBMS or blank for the other UEs). In another example, a subframe is configured as a valid and MBSFN subframe for eMTC UEs, but the subframe is configured as a long CP eMBMS or blank subframe for other UEs. Narrowband CRS is transmitted in symbol 0 in the subframe in the 6 RB narrowband region. Thus, since the subframe is configured differently for the eMTC UEs and the other UEs, it may be ambiguous whether are RS are transmitted in the subframe and/or the bandwidth of the RS.

The following examples of subframe configurations for NB-IoT may result in an ambiguity for the UE as to the presence of RS and/or the bandwidth used sending for the RS in the subframe. In an example, a subframe may configured as a valid and non-MBSFN subframe for NB-IoT UEs with the same-PCI indication set to ‘1’; but it is configured as a MBSFN subframe, a long CP eMBMS subframe, or a blank subframe for other UEs. Narrowband CRS is transmitted in symbols 4, 7, 11 (also in symbol 0 in the case that the subframe is configured as eMBMS or blank for the other UEs) in the subframe in the 1 RB narrowband region. In another example, a subframe is configured as a valid and MBSFN subframe for NB-IoT UEs, but the subframe is configured as a long CP eMBMS or blank subframe for other UEs. Narrowband CRS is transmitted in symbol 0 in the subframe in the 1 RB narrowband region. Thus, since the subframe is configured differently for the NB-IoT UEs and the other UEs, it may be ambiguous whether are RS are transmitted in the subframe and/or the bandwidth of the RS.

Accordingly, there may be ambiguity between the bandwidth of RS assumed by the UE and the actual bandwidth of the RS transmitted by the BS. For example, the BS may transmit 6 RB CRS in an eMTC narrowband; however, the UE may assume 8 RB to 10 RB CRS transmitted. As another example, the BS may transmit 1 RB CRS in an NB-IoT narrowband; however, the UE, may assume 3 RB to 10 RB CRS transmitted.

Aspects of the present disclosure provide techniques that may help eliminate such ambiguity between the UE and BS regarding presence of RS in a subframe and/or a bandwidth of the transmitted RS.

FIG. 11 illustrates example operations 1100 for wireless communications, in accordance with certain aspects of the present disclosure. Operations 1100 may be performed, for example, by a UE (e.g., UE 120) operating in a narrowband region (e.g., 6 RB for eMTC or 1 RB for NB-IoT) of a wider system bandwidth (for example, an eMTC UE or NB-IoT UE). Operations 1100 begin, at 1102, by determining at least one of: a presence of one or more reference signals (RS) in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region. At 1104, the UE monitors for the one or more RS based on the determination.

FIG. 12 illustrates example operations 1200 for wireless communications, in accordance with certain aspects of the present disclosure. Operations 1200 may be performed, for example, by a BS (e.g., BS 110) for communication with a UE operating in a narrowband region of a wider system bandwidth. Operations 1200 may be complementary operations by the BS to the operations 1100 performed by the UE. Operations 1200 begin, at 1202, by determining at least one of: a presence of one or more RS in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region. At 1204, the BS transmits the one or more RS in at least the determined bandwidth.

According to certain aspects, a standard (e.g., a 3GPP wireless telecommunications standard) may mandate that a reference signals (e.g., CRS) is transmitted at a particular bandwidth (e.g., a fixed bandwidth), BW=X. The mandated bandwidth for the RS may be a wider bandwidth than the nominal narrowband bandwidth. For example, X may be greater than 6 RBs for eMTC and/or greater than 1 RB for NB-IoT, with the exception of the narrowband being at the LTE channel edge (in which case the bandwidth may be smaller). In aspects, the bandwidth X may be expressed in number of RBs, subcarriers, Hz, or other frequency granularity/unit.

According to certain aspects, the UE may be signaled (receive/be indicated) an allowed maximum bandwidth assumption, for example, from the BS. The signaled maximum allowed bandwidth assumption may be subframe index dependent or subframe index independent. In other words, the allowed maximum bandwidth assumption may be the same for all subframes or may be different per-subframe. The signaling can be broadcast, for example, in a system information block (SIB). Alternatively, the signaling can be unicast, for example, radio resource control (RRC). In another alternative, the signaling can be both broadcast and unicast, for example, the information in the SIB may be used for paging/SIB acquisition/random access and the RRC for unicast.

According to certain aspects, if the bandwidth of the RS (e.g., CRS) is larger than the nominal narrowband bandwidth, the BS may configure the narrowbands (if more than one narrowband) to be adjacent, in order to reduce overhead.

For the options described above, there may be two types of subframes: “normal” subframes and “blank/MBSFN/eMBMS” subframes. In “normal” subframe, the UE may assume that the RS (e.g., CRS) is transmitted over the total bandwidth (e.g., over 10 MHz in a 10 MHz cell). In “blank/MBSFN/eMBMS” subframes, the UE may assume that the RS is present in a reduced bandwidth (e.g., less than the total bandwidth).

According to certain aspects, for NB-IoT (e.g., in lean carrier type or new carrier type), the BS may always set the same-PCID indicator to “false” (e.g., to “0”), or may set the operating mode to standalone/guard band—even when it is in-band. This may prevent the UE from assuming anything about the CRS, which may avoid ambiguities.

The bandwidth used for RS may apply to CRS in the whole subframe (in the case of non-MBSFN subframes) or the first symbol of the subframe (in the case of MBSFN subframes).

According to certain aspects, the UE may assume (e.g., determine) whether the RS (e.g., CRS) is present or absent in the subframe (and/or the corresponding bandwidth of the RS) based on the channel monitoring and/or decoding assumption. For example, if the UE is monitoring MPDCCH and/or decoding PDSCH in a subframe, the UE may assume that the RS is present (potentially with reduced bandwidth) in the subframe. If the UE does not have any MPDCCH or PDSCH in the subframe, the UE may assume that the RS is not present in the subframe or is present at a reduced bandwidth. The assumption may also be based on other factors, for example, in subframes 0 and 5, the UE may assume that there is always CRS, and in other subframes the UE may assume based on the monitoring and/or decoding in the subframe.

In some cases, for example, if MTC is deployed in new carrier type/carrier that more MBSFN subframes (e.g., than legacy carrier), the UE (e.g., a new type of UE) may receive information in subframes without CRS, whereas legacy UEs may receive information in subframes always with CRS (e.g., legacy MBSFN subframes). In some cases, a random access response (RAR) message, a RACH message 4, and/or a paging message (contention resolution) may be demodulation reference signal (DMRS) based instead of CRS based. In some cases, the BS may signal in the SIB whether DMRS or CRS based transmission is used.

According to certain aspects, for random access (e.g., RAR/RACH Msg. 4) and/or paging, different PRACH resources may be provided for UEs (e.g., legacy UEs) that expect to receive CRS-based transmissions than for UEs that support DMRS based reception (e.g., in addition to support for receiving CRS-based transmissions). For example, legacy UEs may use a first set of PRACH resources, and receive random access message and/or paging based on CRS, while the UEs supporting DMRS may use a second set of PRACH resources. Thus, different sets of UEs may monitor different resources for random access messages and/or paging messages.

According to certain aspects, various parameters may be different for UEs with different capabilities. Different paging occurrence, paging frames (PF), paging occasions (PO) may be used for the different UEs. Different physical radio network temporary identifiers (P-RNTI) may also be used for the different UEs. For example, the UEs supporting DMRS may monitor for a new P-RNTI (e.g., in addition the legacy P-RNTI), and legacy UEs (supporting CRS based only) may only monitor the legacy P-RNTI. Different narrowbands may also be used by the different UEs. In some cases, the mobile management entity (MME) may store the capability of the UEs to receive DMRS-based broadcast and may send this information to the BS in a paging message. In aspects, the transmission mode (DMRS or CRS), frequency location, time location, repetition level, and/or P-RNT of messages such as system information, random access response, and/or RRC configuration message may be based on the UE capability. In these examples, the assumption on CRS for legacy UEs may follow the RS bandwidth determination options descried above.

Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from the context, the phrase, for example, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, for example the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. As used herein, reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” For example, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form. Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c). As used herein, including in the claims, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

As used herein, the term “identifying” encompasses a wide variety of actions. For example, “identifying” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “identifying” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “identifying” may include resolving, selecting, choosing, establishing and the like.

In some cases, rather than actually communicating a frame, a device may have an interface to communicate a frame for transmission or reception. For example, a processor may output a frame, via a bus interface, to an RF front end for transmission. Similarly, rather than actually receiving a frame, a device may have an interface to obtain a frame received from another device. For example, a processor may obtain (or receive) a frame, via a bus interface, from an RF front end for transmission.

The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.

The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in Figures, those operations may be performed by any suitable corresponding counterpart means-plus-function components.

For example, means for determining, means for monitoring, means for processing, means for performing, means for transmitting, means for communicating, means for receiving, means for sending, and/or means for signaling may include one or more processors, transmitters, receivers, antennas, and/or other elements of the user equipment 120 and/or the base station 110 illustrated in FIG. 2.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or combinations thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as hardware, software, or combinations thereof. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. One or more aforementioned devices or processors may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination thereof. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, phase change memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more exemplary designs, the functions described may be implemented in hardware, software, or combinations thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD/DVD or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. 

What is claimed is:
 1. A method for wireless communications by a user equipment (UE) operating in a narrowband region of a wider system bandwidth, comprising: determining at least one of: a presence of one or more reference signals (RS) in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region; and monitoring for the one or more RS in the subframe based on the determination.
 2. The method of claim 1, wherein the one or more RS comprise at least one cell-specific reference signal (CRS).
 3. The method of claim 1, wherein the determination is based on signaling received by the UE.
 4. The method of claim 1, wherein the determination is based, at least in part, on a subframe index.
 5. The method of claim 1, wherein the determination is based on a fixed bandwidth defined for the one or more RS.
 6. The method of claim 1, wherein the determination is based, at least in part, on a location of the narrowband region within the wider system bandwidth.
 7. The method of claim 1, wherein the determination is based, at least in part, on whether the UE is receiving or monitoring for a downlink channel in the subframe.
 8. The method of claim 1, wherein the determination is based, at least in part, on a type of the subframe.
 9. The method of claim 1, further comprising: determining one or more parameters for receiving at least one of: system information, a paging message, a random access response (RAR) message, or a radio resource control (RRC) configuration message based, at least in part, on the determination; and monitoring for the at least one of: the system information, the paging message, the RAR message, or the RRC configuration message according to the determined one or more parameters.
 10. The method of claim 9, wherein the one or more parameters comprise at least one of: a transmission mode, a frequency location, a time location, a repetition level, or a Radio Network Temporary Identifier (RNTI).
 11. The method of claim 10, wherein the transmission mode comprises a demodulation reference signal (DMRS) based transmission mode or a cell-specific reference signal (CRS) based transmission mode.
 12. The method of claim 9, further comprising: determining one or more physical random access channel (PRACH) resources based on at least of: a transmission mode capability of the UE or a type of the UE; and monitoring for a RAR based on the determined parameters.
 13. A method for wireless communications by a base station (BS) for communication with a user equipment (UE) operating in a narrowband region of a wider system bandwidth, comprising: determining at least one of: a presence of one or more reference signals (RS) in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region; and transmitting the one or more RS in the subframe in at least the determined bandwidth.
 14. The method of claim 13, wherein one or more RS comprise at least one cell-specific reference signal (CRS).
 15. The method of claim 13, further comprising: transmitting signaling to the UE indicating the at least one of: the presence of the one or more RS in the subframe or the bandwidth of the one or more RS.
 16. The method of claim 13, wherein the determination is based, at least in part, on a subframe index.
 17. The method of claim 13, wherein the determination is based on a fixed bandwidth defined for the one or more RS.
 18. The method of claim 13, wherein the determination is based, at least in part, on a location of the narrowband region within the wider system bandwidth.
 19. The method of claim 14, wherein the determination is based, at least in part, on a type of the subframe.
 20. The method of claim 13, further comprising: determining one or more parameters for transmitting to the UE at least one of: system information, a paging message, a random access response (RAR) message, or a radio resource control (RRC) configuration message based, at least in part, on the determination; and transmitting the at least one of: the system information, the paging message, the RAR message, or the RRC configuration message according to the determined one or more parameters.
 21. The method of claim 20, wherein the one or more parameters comprise at least one of: a transmission mode, a frequency location, a time location, a repetition level, or a Radio Network Temporary Identifier (RNTI).
 22. The method of claim 21, wherein the transmission mode comprises a demodulation reference signal (DMRS) based transmission mode or a cell-specific reference signal (CRS) based transmission mode.
 23. The method of claim 22, further comprising: communicating with the UE using the DMRS based transmission mode using a first set of resources if the UE is a first type of UE; and communicating with the UE using the CRS based transmission mode using a second set of resources if the UE is a second type of UE.
 24. The method of claim 13, further comprising: determining resources for receiving a radio resource control (RRC) connection request message from the UE based, at least in part, on a capability of the UE.
 25. An apparatus for wireless communications by a user equipment (UE) operating in a narrowband region of a wider system bandwidth, comprising: means for determining at least one of: a presence of one or more reference signals (RS) in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region; and means for monitoring for the one or more RS in the subframe based on the determination.
 26. The apparatus of claim 25, wherein the determination is based on signaling received by the UE.
 27. The apparatus of claim 25, wherein the determination is based, at least in part, on a subframe index.
 28. The apparatus of claim 25, wherein the determination is based on a fixed bandwidth defined for the one or more RS.
 29. An apparatus for wireless communications by a base station (BS) for communication with a user equipment (UE) operating in a narrowband region of a wider system bandwidth, comprising: means for determining at least one of: a presence of one or more reference signals (RS) in a subframe or a bandwidth of the one or more RS, wherein the bandwidth of the one or more RS is greater than or equal to a bandwidth of the narrowband region; and means for transmitting the one or more RS in the subframe in at least the determined bandwidth.
 30. The apparatus of claim 29, further comprising: means for transmitting signaling to the UE indicating the at least one of: the presence of the one or more RS in the subframe or the bandwidth of the one or more RS. 